Asymmetric domino synthesis of indanes bearing four contiguous stereocentres catalyzed by sub-mol% loadings of a squaramide in minutes

Synthesis of chiral systems featuring the pyrrole unit: a review

Synthetic strategies towards pyrroles within chiral frameworks are summarised, focussing on reports published 2010-2023. The synthesis of pyrroles featuring substituents bearing chiral centres are summarised, as are those whereby pyrroles are located within axially chiral systems courtesy of restricted bond rotation.

Organocatalytic Asymmetric Synthesis of Carbo- and Oxacyclic Seven-Membered Bridged Biaryls via Nucleophile-Dependent Switchable Domino Processes

We disclose herein a highly diastereo- and enantioselective divergent synthesis of seven-membered biaryl-bridged carbo- and oxacyclic frameworks by utilizing the catalytic ability of bifunctional hydrogen-bonding squaramide organocatalysts. Starting with the same biaryl substrate bearing two distinct acceptor sites and by choosing soft or hard nucleophiles, we readily accessed the dibenzocycloheptanes or 5,7-dihydrodibenzo[c,e]oxepines bearing multiple elements of chirality via a domino 1,4/1,2-addition or 1,2/oxa-Michael addition sequence, respectively.

Triflic Acid-Catalyzed Synthesis of Indole-Substituted Indane Derivatives via In Situ Formed Acetal-Facilitated Nucleophilic Addition and 4π-Electron-5-Carbon Electrocyclization Sequence

An efficient protocol for the synthesis of indole-substituted indanes from o-alkenylbenzaldehydes under acetalization conditions has been presented. The cyclization occurs via a nucleophilic addition of indole on the oxacarbenium ion generated from acetal formed under the reaction condition followed by a conrotatory 4π-electrocyclization reaction, which takes care of the exclusive diastereoselectivity observed during the cyclization step. Olefin geometry of o-alkenylbenzaldehyde and the amount of indole play a decisive role in the success of this cyclization process.

Copper-catalyzed asymmetric tandem borylative addition and aldol cyclization

A highly enantioselective asymmetric copper-catalyzed tandem conjugate addition/aldol cyclization of electron-deficient olefins with B₂pin₂ was developed, which provided a rapid access to indanes bearing three consecutive chiral stereogenic centers.

N-Heterocyclic carbene-catalyzed diastereoselective synthesis of sulfenylated indanes via sulfa-Michael-Michael (aldol) cascade reactions

N-Heterocyclic carbene (NHC)-catalyzed diastereoselective synthesis of multisubstituted sulfenylated indanes has been developed. In the presence of 1 mol% NHC, various thiols underwent the sulfa-Michael-Michael cascade reaction with benzenedi(enones) efficiently to form the carbon-sulfur bond and construct sulfenylated indanes in good to excellent yields with high diastereoselectivity. In addition, the NHC-catalyzed sulfa-Michael-aldol cascade reaction between o-formyl chalcone and thiols has also been demonstrated to afford sulfenylated indanes with a free hydroxyl group in moderate yields and good diastereoselectivity.

Asymmetric Synthesis of Spirocyclopentane Oxindoles Containing Four Consecutive Stereocenters and Quaternary α-Nitro Esters via Organocatalytic Enantioselective Michael-Michael Cascade Reactions

An enantioselective domino Michael-Michael reaction of nitroolefins and 2-nitro-3-arylacrylates has been established, which provided a series of spirocyclopentane oxindoles with four consecutive stereocenters including quaternary α-nitro esters with good yields (up to 73%) and excellent enantioselectivities (up to 97% ee). The reaction was realized and optimized with the aid of a chiral squaramide-amine catalyst. The structures of 11 products were confirmed by single-crystal X-ray diffraction analysis.

Organocatalytic asymmetric Michael addition between 3-subsituted oxindoles and enals catalyzed by camphor sulfonyl hydrazine

3,3-Disubstituted oxindoles containing vicinal stereogenic carbon centers have been synthesized through organocatalytic asymmetric Michael addition between 3-substituted oxindoles and enals catalyzed by chiral camphor sulfonyl hydrazines (CaSHs).

N-Heterocyclic carbene-catalyzed β-addition of enals to 3-alkylenyloxindoles: synthesis of oxindoles with all-carbon quaternary stereocenters

The N-heterocyclic carbene-catalyzed β-addition of enals to 3-alkylenyloxindoles was developed. All of the β-aryl, β-alkenyl and β-alkyl enals worked well for the reaction to give the corresponding 3,3-disubstituted oxindoles bearing contiguous all-carbon quaternary and tertiary stereocenters in good yields with moderate to high diastereoselectivities and excellent enantioselectivities.

Organocatalytic Strategies for the Synthesis of Cyclopenta-Fused Arenes and Heteroarenes

Cyclopentanoids are omnipresent in natural products and pharmaceutically relevant compounds. Among them, cyclopenta-fused arenes and heteroarenes possess impressive biological properties and play significant role in materials science. Consequently, several notable methods have been developed for their synthesis over the years. In this review, we mainly described metal-free and organocatalytic approaches that led to the construction of pentannulated arenes and heteroarenes.

Synthesis of spiro-tetrahydrothiopyran-oxindoles by Michael–aldol cascade reactions: discovery of potential P53-MDM2 inhibitors with good antitumor activity

Novel one-pot Michael–aldol cascade reactions were used to efficiently construct spiro-tetrahydrothiopyran-oxindoles with good in vitro antitumor activity.

Enantioselective syntheses of indanes: from organocatalysis to C–H functionalization

The indanyl core is ubiquitous in a large variety of drugs and natural products. Remarkable recent progress has been accomplished in the step-economical assembly of functionalization of chiral indanes by means of enantioselective catalysis, with major progress being achieved in organocatalysis and C–H activation chemistry.

Asymmetric synthesis of functionalized cyclohexanes bearing five stereocenters via a one-pot organocatalytic Michael-Michael-1,2-addition sequence

A highly stereoselective one-pot organocatalytic procedure involving a Michael–Michael–1,2-addition sequence provides an efficient access to fully substituted cyclohexanes bearing five contiguous stereocenters in good yields and excellent stereoselectivities.

A highly stereoselective one-pot procedure involving an enantioselective Michael addition promoted by low loading of an amino-squaramide catalyst followed by an achiral base catalyzed domino Michael–Knoevenagel-type 1,2-addition sequence provides efficient access to fully substituted cyclohexanes bearing five contiguous stereogenic centers in good yields (68–86%) and excellent stereoselectivities (>30 : 1 dr and 96–99% ee).

Organocatalytic Asymmetric Domino Michael/Henry Reaction of Indolin-3-ones with o-Formyl-β-nitrostyrenes

A highly diastereo- and enantioselective domino Michael/Henry reaction of 1-acetylindolin-3-ones with o-formyl-(E)-β-nitrostyrenes catalyzed by low loading of a quinine-derived amine-squaramide provides the corresponding indolin-3-one derivatives bearing four adjacent stereogenic centers in good to high yields and with excellent stereoselectivities.

Organocatalytic Asymmetric Synthesis of Dihydroisoquinolinones via a One-Pot Aza-Henry-Hemiaminalization-Oxidation Sequence

The asymmetric organocatalytic one-pot synthesis of trans-3,4-disubstituted 3,4-dihydroisoquinolin-1(2H)-ones is described. Starting from 2-(nitromethyl)benzaldehydes and various N-protected aldimines, 5 mol% of a quinine-based squaramide organocatalyst was used to synthesize the title compounds as virtually single diastereomers via an aza-Henry-hemiaminalization-oxidation sequence. Moderate to good yields (39-78%) and moderate to very good enantioselectivities (40-95% ee) were reached.

Asymmetric tandem reactions of N-sulfonylimines and α,β-unsaturated aldehydes: an alternative reaction pathway to that of using saturated aldehydes

An organocatalyzed asymmetric tandem reaction of cyclic N-sulfonylimines and α,β-unsaturated aldehydes was developed, undergoing an alternative reaction pathway while affording similar piperidines to that of reactions involving saturated aldehydes.

Asymmetric synthesis of highly functionalized tetrahydropyrans via a one-pot organocatalytic Michael/Henry/ketalization sequence

A diastereo- and enantioselective Michael/Henry/ketalization sequence to functionalized tetrahydropyrans is described. The multicomponent cascade reaction uses acetylacetone or β-keto esters, β-nitrostyrenes, and alkynyl aldehydes as substrates affording tetrahydropyrans with five contiguous stereocenters. Employing a bifunctional quinine-based squaramide organocatalyst, the title compounds are obtained in moderate to good yields (27-80%), excellent enantiomeric excesses (93-99% ee), and high diastereomeric ratios (dr > 20:1) after one crystallization.

On the mechanism of bifunctional squaramide-catalyzed organocatalytic Michael addition: a protonated catalyst as an oxyanion hole

A joint experimental-theoretical study of a bifunctional squaramide-amine-catalyzed Michael addition reaction between 1,3-dioxo nucleophiles and nitrostyrene has been undertaken to gain insight into the nature of bifunctional organocatalytic activation. For this highly stereoselective reaction, three previously proposed mechanistic scenarios for the critical CC bond-formation step were examined. Accordingly, the formation of the major stereoisomeric products is most plausible by one of the bifunctional pathways that involve electrophile activation by the protonated amine group of the catalyst. However, some of the minor product isomers are also accessible through alternative reaction routes. Structural analysis of transition states points to the structural invariance of certain fragments of the transition state, such as the protonated catalyst and the anionic fragment of approaching reactants. Our topological analysis provides deeper insight and a more general understanding of bifunctional noncovalent organocatalysis.